1. Field of the Invention
The present invention relates to a power amplifying circuit of a transmitter in a mobile terminal and, more particularly, to a voltage gain control circuit in a mobile terminal, which is capable of acquiring a variable voltage gain.
2. Description of the Related Art
Mobile terminal technology is continuously developing due to the development of the IT technology. Communication technology is developing from first generation technology AMPS (advanced mobile phone service), second generation technology CDMA (code-division multiple access) and GSM (global system for mobile communication), to third generation technology WCDMA (wideband CDMA).
In comparison to the first generation AMPS mobile terminals, the second generation CDMA (code-division multiple access) and GSM (global system for mobile communication) mobile terminals have been reduced in size, and have increased in total usage time and call quality.
In the third generation technology WCDMA (wideband CDMA), it is possible to provide not only voice data transmission services but also image information transmission services. Data transmission speeds have been greatly increased over the second generation CDMA and GSM terminals.
However, for the high-speed transmission of data, the power consumption of a mobile terminal has, also increased, which caused reduction in, total usage time of the battery and, problem in the mobile terminals.
FIG. 1A is a block diagram illustrating an embodiment of a conventional power amplifying circuit. As shown in FIG. 1A, power amplifier 100 amplifies a transmission signal according to a predetermined voltage gain. Then, power amplifier 100 sends the amplified signal to a duplexer, (not shown) to transmit the signal, over the air. Transmission signal processing block (T×IC) 120 performs an RF transformation of a baseband processing signal received from transceiver controller 110, and then inputs the transformed signal to power amplifier 100.
Battery 130 supplies a uniform driving voltage to the power amplifier 100. Transceiver controller 110 sends either an on or off control signal to power amplifier driving switch 140 according to a power amplifier driving signal.
When power amplifier driving switch 140 turns on, power amplifier control voltage Vcon is sustained at a uniform voltage level and is supplied to power amplifier 100. Accordingly, in FIG. 1A, power amplifier 100 has a fixed voltage gain that is determined by a constant voltage from battery 130 and power amplifier control voltage Vcon.
FIG. 1B is a block diagram illustrating another embodiment of a conventional power amplifying circuit. Unlike FIG. 1A, FIG. 1B shows that the power amplifier control voltage Vcon is controlled by a voltage gain control signal from the transceiver controller 110.
As shown in FIG. 1B, power amplifier 100 amplifies a transmission signal according to the voltage gain that is determined by the voltage gain control signal of transceiver controller 110. In this case, a PDM (pulse density modulation) signal may be used as the voltage gain control signal.
Transmission signal processing block (T×IC) 120 performs an RF transformation of a baseband processing signal received from the transceiver controller 110, and then inputs the transformed signal to the power amplifier 100.
The battery 130 supplies a uniform driving voltage to the power amplifier 100. The power amplifier driving switch 140 sends either an on or off control signal to power amplifier 100. Filter 150 reduces the possibility of a voltage gain error by eliminating unnecessary noises.
When the power amplifier driving switch 140 turns on, the power amplifier control voltage Vcon is determined by the voltage gain control signal of the transceiver controller 110. Thus, the voltage gain of power amplifier 100 varies as the voltage gain control signal varies.
FIG. 1C is a block diagram illustrating still another embodiment of a conventional power amplifying circuit. In FIG. 1C, unlike to FIG. 1A and FIG. 1B, the power amplifier control voltage Vcon of the power amplifier 100 is supplied through a separate voltage scaling circuit 160. In other words, the power amplifier control voltage Vcon is a transformed value of the voltage gain control signal of the transceiver controller 110. The transmission signal processing block 120 transforms the baseband processing signal and the voltage gain control signal into a transmission level, and then inputs the transformed signals to the power amplifier 100.
Meanwhile, the voltage scaling circuit 160 transforms the voltage gain control signal into a signal for acquiring a desired voltage gain, and then inputs the transformed signal to the power amplifier 100. The power amplifier 100 can acquire a desired voltage gain by the power amplifier control voltage Vcon.
The battery 130 supplies a source voltage to the power amplifier 100. The transceiver controller 110 sends an on or off control signal to the power amplifier driving switch 140 according to the power amplifier driving signal. The transceiver controller 110 supplies a voltage gain control signal to the power amplifier 100 through the filter 150 for eliminating noises to avoid the occurrence of a voltage gain error.
In FIG. 1C, the voltage gain control signal supplied by the transceiver controller 110 determines the output signal of the transmission signal processing block 120 and the output signal of the voltage scaling circuit 160. The voltage gain varies according to the output signals. Thus, a desired voltage gain can be acquired by controlling the output signals of transmission signal processing block 120 and voltage scaling circuit 160.
In the prior art, a battery voltage decreases with the lapse of time, and thus, the efficiency of the power amplifier also gradually decreases. The decrease in the efficiency of the power amplifier leads to a reduction in time the battery can be used (i.e., battery life) and creates the heating problem of a mobile terminal. Accordingly, in the prior art, the efficiency of power amplifier varies, based on the battery voltage variation.
Table 1 shows a current flow according to the relation of the battery voltage Vbat and the power amplifier control voltage Vcon, when the battery voltage Vbat is applied as an external source voltage Vcc and no input signal is applied.
TABLE 1Vcon (V)1.61.71.81.92.02.12.22.32.42.5Vcc(V)3.00.0140.0160.0190.0210.0230.0260.0280.0300.0330.0353.20.0140.0170.0200.0220.0250.0270.0290.0310.0330.0363.40.0150.0180.0210.0240.0260.0280.0300.0330.0350.0373.60.0170.0190.0220.0250.0270.0300.0320.0340.0360.0383.80.0170.0200.0230.0260.0290.0310.0340.0360.0380.0404.00.0180.0210.0250.0280.0300.0330.0360.0380.0400.0424.20.0180.0220.0250.0290.0320.0340.0370.0400.0420.0444.40.0190.0220.0260.0290.0330.0360.0380.0410.0440.046
As shown in table 1, a uniform current flows according to the relation of external source voltage Vcc and the power amplifier control voltage Vcon, when no input is applied.
In this case, experiments show that the efficiency of the power amplifier is highest when the external source voltage Vcc is between 3.4 V and 4.2 V. In particular, the difference of the efficiency is over a few percentage points (%) when the battery voltages are 4.2V and 3.2V.